public abstract class GenericJob implements Database.Batchable<SObject>, Database.Stateful {
    String query;

    public void setQuery(String query) {
        this.query = query;
    }

    public String getQuery()
    {
        return query;
    }

    public Database.QueryLocator start(Database.BatchableContext context) {
        return Database.getQueryLocator(query);
    }

    public abstract void execute(Database.BatchableContext context, List<sObject> scope);

    public void finish(Database.BatchableContext context) {
        ... // my own finish logic here
        doFinish(context);
    }

     public abstract void doFinish(Database.BatchableContext context); // user defined execute logic
}